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Biomedical subjects

S White

Publications and source records attributed to S White.

At least 145 records · Page 8Linked to original sources
PubMed1996

Effects of the A.T/T.A degeneracy of pyrrole--imidazole polyamide recognition in the minor groove of DNA.

Pairing rules have been developed to predict the sequence specificity of minor groove binding polyamides containing pyrrole (Py) and imidazole (Im) amino acids. An Im/Py pair distinguishes G.C from C.G and both of these from A.T/T.A base pairs. A Py/Py pair appears not to distinguish A.T from T.A base pairs. To test the extent of this degeneracy, the affinity and binding orientation of the hairpin polyamide ImPyPy-gamma-PyPyPy-beta-Dp were measured for eight possible five base pair 5'-TG(A,T)(3)-3' match sites. Affinity cleavage experiments using a polyamide with an EDTA.Fe(II) moiety at the carboxy terminus, ImPyPy-gamma-PyPyPy-beta-Dp-EDTA.Fe(II), are consistent with formation of an oriented 1:1 hairpin polyamide complex at all eight 5'-TG(A,T)(3)-3' binding sites [20 mM HEPES, 200 mM NaCl, 50 mg/ml glycogen, pH 7.0, 22 degrees C, 5 mM DTT, 1 mM Fe(II)]. Quantitative DNase I footprint titration experiments reveal that ImPyPy-gamma-PyPyPy-beta-Dp binds all eight 5'-TG(A,T)(3)-3' target sites with only a 12-fold difference in the equilibrium association constants between the strongest site, 5'-TGTTT-3' (Ka = 2.1 x 10(8) M-1), and the weakest site, 5'-TGAAT-3' (Ka = 1.8 x 10(7) M-1) (10 mM Tris.HCl, 10 mM KCl, 10 mM MgCl2, 5 mM CaCl2, pH 7.0, 22 degrees C). This relatively small range indicates that the Py/Py pair is approximately degenerate for recognition of A,T base pairs, affording generality with regard to targeting sequences of mixed A.T/T.A composition.

Base Composition↗
PubMed1996

Microsatellite instability and the role of hMSH2 in sporadic colorectalcancer.

Microsatellite instability (MSI) occurs in most tumours from patients with hereditary non-polyposis colorectal cancer (HNPCC) and in around 17% of sporadic colorectal cancers. Germline defects in mismatch repair (MMR) genes are responsible for the majority of large HNPCC families, with hMSH2 accounting for at least 50%. MMR gene defects also occur in a small proportion of sporadic colorectal tumours with MSI. Here we report a systematic analysis of mismatch repair deficiency in 215 Scottish patients with sporadic colorectal tumours. We found that 16.4% of tumours exhibited MSI; survival analysis by Cox proportional hazards method showed a substantial survival advantage for patients with tumours showing MSI, independent of other prognostic factors. Tumours with MSI were screened for hMSH2 mutations and although 61% were found to have alterations, of these only 1/24 was exonic. The majority of these changes were reductions in length at intronic mononucleotide tracts and we postulate that these alterations are the result of a genetic defect elsewhere, although they may compromise hMSH2 function as a second step in tumourigenesis. Our findings indicate that instability confers an improved prognosis in colorectal cancer and, despite the fact that these two groups of tumours share similar biological characteristics, the genetic basis of HNPCC and sporadic colorectal cancer with MSI is different.

Base Sequence↗
PubMed1996

Functional analysis of human/chicken transferrin receptor chimeras indicates that the carboxy-terminal region is important for ligand binding.

Chimeric human/chicken transferrin receptors have been constructed using the polymerase chain reaction. Different regions of the 671-residue external domain of the human transferrin receptor were replaced by the corresponding sequences from the chicken transferrin receptor. As chicken transferrin receptors do not bind human transferrin, functional analysis of such chimeric receptors provides an approach to define the ligand-binding site of the human transferrin receptor. Four of 16 chimeric human/chicken transferrin receptors expressed in chick embryo fibroblasts were efficiently transported to the plasma membrane and displayed on the cell surface. Studies of the four chimeric receptors indicated that binding of human transferrin was abolished if the carboxy terminal 192 amino acids of the human transferrin receptor (residues 569-760) were replaced with the corresponding region from the chicken transferrin receptor. Further, a chimeric receptor in which the carboxy-terminal 72 residues were derived from the chicken transferrin receptor exhibited a 16-fold decrease in binding affinity for human transferrin. In contrast, analysis of the other two chimeric receptors showed that 340 amino acids of the human transferrin receptor external domain more proximal to the transmembrane region (residues 151-490) could be replaced with the corresponding region from the chicken transferrin receptor without loss of high-affinity ligand binding. In contrast, two mAbs against the human transferrin receptor external domain, B3/25 and D65.3, that do not compete with transferrin binding, do not bind the chimeric transferrin receptors in which the membrane proximal part is replaced by chicken sequences, while they do bind the two other chimeric transferrin receptors with high affinity. These data indicate that sequence differences in the carboxy-terminal region of human and chicken transferrin receptor external domains are important for the species specificity of transferrin binding and imply that this portion of the human transferrin receptor is critical for ligand binding.

Animals↗
PubMed1996

Testicular microlithiasis: a benign condition with a malignant association.

Testicular microlithiasis (TM), which usually affects both testes, is diagnosed primarily by ultrasound. TM has been found to be associated with benign conditions but has also been reported in association with testicular cancer. Echographically, TM is manifested by diffuse, punctate, non-shadowing, hyperechoic foci within the testicular parenchyma. To date, more than 80 cases of TM have been documented sonographically or pathologically; 25 of them have demonstrated an association with pathologically proven testicular cancer (p < 0.05). Thirty-two cases were associated with infertility/subfertility (p < 0.05). We believe the finding of TM on ultrasound should heighten the radiologist's suspicion of testicular malignancy. If no malignancy is identified on initial evaluation including CT of the chest and abdomen, close clinical follow-up with periodic (every 6 to 12 months) scrotal ultrasound examination is probably indicated.

Adolescent↗
PubMed1996

Germline APC mutation (Gln1317) in a cancer-prone family that does not result in familial adenomatous polyposis.

Germline mutations of the adenomatous polyposis coli gene are associated with the dominantly inherited syndrome of familial adenomatous polyposis. Somatic mutations in this gene are an early event in sporadic colorectal tumorigenesis. Here we report a family with genetic characteristics that do not conform exactly to either of these situations. The index case and three siblings presented with colorectal cancer, and another sibling had lung cancer. There was no evidence of colorectal cancer susceptibility in previous generations, although one case of gastric cancer was observed. Using restriction fragment length polymorphism, single-strand conformational polymorphism, and sequencing analysis, we screened each living family member for alterations in the mutation cluster region of exon 15 of the APC gene. A constitutional single base pair substitution at codon 1317 was observed in two of the siblings with colorectal cancer, but neither exhibited any colonic features typical of FAP nor an early onset of cancer. This constitutional change is a missense mutation and therefore does not result in the truncation of the APC protein, the most commonly observed result of mutation in this gene. We present evidence that this change is not a polymorphism and may be capable of conferring a growth advantage. This particular germline APC mutation does not completely cosegregate with cancer in this family; therefore, we conclude that another gene locus may be responsible for the increased cancer risk observed.

Adenocarcinoma↗
PubMed1996

Physician profiling: applications for the Robert Wood Johnson Profiling Project database.

An overview of the applications and limitations of the Center for Research in Ambulatory Health Care Administration (CRAHCA) Profiling Project database funded by The Robert Wood Johnson Foundation is presented. The Profiling Project collects data from 77 practices and links organizational, provider, and patient demographics to administrative data. The Project's database has the capacity (1) to profile physicians based on the Resource Based Relative Value Scale (RBRVS) relative value units as a measure of work and (2) to identify practice patterns as defined by procedures used by physicians with the same diagnosis. The Project will further explore variations between physicians and specialties based on systems of care, physician specialty, and patient differences. The comparative reports generated from these data provide comparisons on selected indicators for participating practices.

Ambulatory Care↗
PubMed1996

A comparison of reusable versus disposable laparoscopic instrument costs.

BACKGROUND: Between 1991 and 1993 a single set of reusable laparoscopic instruments was used to perform 404 cholecystectomies, 102 hernia repairs and 66 advanced procedures. Disposable instruments were used only when no suitable reusable instrument was available or when reusable instruments were not working to the satisfaction of the surgeon. METHODS: The cost of performing those laparoscopic operations using this policy was calculated by adding the purchase cost, the maintenance costs and the repair and replacement costs of the reusable instruments. To this figure was added the cost of disposable instruments which were used instead of reusable instruments during the study period. RESULTS: The total cost was $253,385, at an average of $443 per case. The cost per case for reusable instruments remained approximately $100 through the 3 years, while the cost per case of disposable instruments fell from almost $600 in 1991 to about $200 in 1993. CONCLUSIONS: Our future policy is to continue using reusable instruments initially, with backup disposable instruments.

Costs and Cost Analysis↗
PubMed1996

Community collaboration: prevention and control of tuberculosis in a homeless shelter.

An urban shelter in Charleston, South Carolina developed and began a tuberculosis (TB) prevention and control plan that addressed the priorities recommended by the Centers for Disease Control and Prevention. After an increase in TB in the shelter in 1992, the local health department, the homeless clinic nurse practitioners, and Medical University of South Carolina College of Nursing faculty and students collaborated with the shelter staff to provide initial mass screenings for contact investigation. They also developed and implemented new policies and procedures for an ongoing TB prevention and control program. The new policies required that guests obtain screening for TB within 7 days of arrival at the shelter and every 6 months thereafter. Also, a public health nurse began providing directly observed therapy twice weekly at the shelter. Of the initial 22 persons who started TB preventive therapy in 1993, 17 (77%) completed therapy. The clinic nurse practitioners, nursing students, and public health nurses had important and defined roles in the mass-screening process, case identification and treatment, policy development and implementation, health education, and establishing methods of communication between the shelter, clinic, and health department. An ongoing health care community collaborative effort may successfully reduce tuberculosis disease in a homeless shelter population.

Communication↗
PubMed1996

Speechreading and speechreading tests: a survey of rehabilitative audiologists.

Members of the Academy of Rehabilitative Audiology were surveyed to determine their views on speechreading and speechreading tests. Although a minority of those surveyed were providing speechreading training, most considered speechreading important but were concerned about the validity and usefulness of speechreading tests. Audiologists felt a need for new speechreading tests in all age groups, ranging from preschool to older adults. Thus, there is a need for new speechreading tests to go along with the new methods of training, such as speech tracking.

Audiology↗
PubMed1996

Local staging of prostatic carcinoma: comparison of transrectal sonography and endorectal MR imaging.

OBJECTIVE: We compared the results of transrectal sonography and endorectal MR imaging in the local staging of prostatic carcinoma. SUBJECTS AND METHODS: 56 patients (mean age, 61.1 +/- 7.3 years) with the diagnosis of prostate cancer who by transrectal sonography had no evidence of gross extracapsular extension underwent endorectal coil MR imaging prior to radical prostatectomy. Imaging findings prospectively evaluated in each patient were cancer laterality, extracapsular extension, and seminal vesicle invasion. Twenty-one of 56 (38%) patients had extracapsular extension on final pathology. A total of 100 sides and five seminal vesicles were involved with cancer, and 27 sides (21 patients, six with bilateral extracapsular extension) demonstrated extracapsular extension. Imaging results were correlated with step-sectioned, radical prostatectomy pathologic data, and statistical analysis was expressed at a p = .05 level of significance. Retrospective readings of the images were used to construct receiver operating characteristic curves for the detection of extracapsular extension. RESULTS: For tumor laterality, transrectal sonography was compared with endorectal coil MR imaging for sensitivity (70% versus 97%; p < .001), specificity (58% versus 58%), positive predictive value (93% versus 95%) and negative predictive value (18% versus 70%). For extracapsular extension, transrectal sonography was compared with endorectal coil MR imaging for the entire prostate and individually for each side of the prostate. The respective results for sensitivity (48% versus 91%, p < .01 and 37% versus 78%, p < .005), specificity (71% versus 49% and 87% versus 73%), positive predictive value (50% versus 51% and 48% versus 48%), and negative predictive value (69% versus 90% and 81% versus 91%). The receiver operating characteristic analysis of retrospective data demonstrated endorectal coil MR imaging to be superior to transrectal sonography in the detection of extracapsular extension. The small number of seminal vesicles involved by cancer (n = 5) precluded meaningful comparisons between the imaging techniques. CONCLUSIONS: Endorectal coil MR imaging is more sensitive but less specific than transrectal sonography for detecting extracapsular extension of carcinoma of the prostate. Both procedures have low positive predictive values yet similarly high negative predictive values when each side of the prostate is assessed independently for extracapsular extension.

Humans↗
PubMed1996

Stress fractures: a review of 180 cases.

OBJECTIVE: To review the cases of stress fracture seen over a 2-year period at a sports medicine clinic. DESIGN: One hundred and eighty cases diagnosed as stress fractures on the basis of clinical picture and radiological evidence were reviewed. The following features of each stress fracture were noted: age, sex, site, sport/activity. SETTING: A sports medicine centre in Melbourne, Australia. PATIENTS: The average age was 21.8 years. Seventy eight of these stress fractures were seen in women, 102 in men. RESULTS: The most common sites of stress fractures were the metatarsal bones (n = 42), tibia (n = 36), fibula (n = 30), tarsal navicular (n = 26) and pars interarticularis (n = 17). The most common sport was track (n = 54). Other common sports activities were jogging/distance running (n = 35), dance (n = 32) and Australian football (n = 14). The distribution of sites of stress fractures varied from sport to sport. Among the track athletes (n = 54), navicular (n = 19), tibia (n = 14) and metatarsal (n = 9) were the most common stress fracture sites. The distance runners (n = 35) predominantly sustained tibia (n = 15), and fibula (n = 8) stress fractures, while metatarsal stress fractures (n = 18) were the most common among dancers. The distribution of sports varied with the site of the stress fracture. In the metatarsal stress fractures (n = 42), dance was the most common activity. Distance running (n = 15) and track (n = 14) were the most common sports in the group to have sustained tibia stress fractures (n = 36). Track athletes (n = 14) were particularly prevalent in the navicular stress fracture group (n = 26). CONCLUSION: The distribution of sites of stress fractures in this study shows some differences from previously published studies.

Adult↗
PubMed1995

Probing the active sites of rat and human cytochrome P450 2E1 with alcohols and carboxylic acids.

Cytochrome P450 2E1 (P450 2E1) catalyzes the biotransformation of many low-molecular-weight compounds including industrial solvents, indoor pollutants, alcohol, and drugs. In order to understand the nature of the P450 2E1 active site, we studied the competitive inhibition of the P450 2E1-catalyzed N-nitrosodimethylamine demethylation by alcohols and carboxylic acids with different alkyl chain lengths. Using microsomes from acetone-treated rats as the enzyme source of P450 2E1, the Ki value for each compound was measured. With primary alcohols and secondary alcohols, the Ki decreased with the increase in the carbon chain length until the carbon number reached 6 or 7; the free energy increment of binding was 0.28 kcal/mol CH2 group. Similar inhibitory effects were also observed with human P450 2E1 heterologously expressed in Hep G2 cells. These results suggest that both rat and human P450 2E1 contain a pocket with hydrophobicity that serves as a binding site for low-molecular-weight substrates. Among a series of carboxylic acids and omega-hydroxycarboxylic acids investigated, dodecanoic acid was the strongest inhibitor (Ki = 22 microM), and 12-hydroxydodecanoic acid had the lowest Ki (320 microM) within the series of omega-hydroxycarboxylic acids. The free energy increment of binding for carboxylic acids was 0.35 kcal/mol CH2 group. 1,10-Decanedicarboxylic acid, which contains a carboxylic group at each end, showed a Ki > 20 mM. We suggest that for optimal interaction of a carboxylic acid moiety with the active site of P450 2E1, the hydrocarbon end of the molecule binds to the substrate binding site, leaving the carboxylic acid group outside of a proposed substrate access channel. The length of optimal substrates such as dodecanoic acid may reflect the length of the substrate access channel and the size of the active site. We estimate that the distance from the opening of the access channel to the oxygenation site is about 15 A. Based on the structural features of P450 2E1 substrates and competitive inhibitors, we propose a conceptual model to illustrate the binding of these molecules in the active site of P450 2E1.

Alcohols↗
PubMed1995

FDG-PET in children and adolescents with partial seizures: role in epilepsy surgery evaluation.

We used FDG-PET to measure interictal glucose metabolism in 16 children and adolescents (mean age 14.7 years) and complex partial seizures (CPS) (mean seizure onset age 5.0 years). Video-EEG localized the epileptic foci. Glucose metabolism was determined in 14 paired anatomic areas using a standard template. PET hypometabolism was defined as greater than 15% asymmetry. Nine of the 13 (69%) patients with a unilateral EEG focus had regional hypometabolism ipsilateral to the epileptogenic zone. Three subjects had bilateral EEG foci; all had nonfocal PET. MRI (15 patients) concurred with EEG and PET in two, and was normal in seven of nine with focal hypometabolism. One of seven patients with normal PET had a focal MRI abnormality. FDG-PET results are similar to those found in adults, but are present earlier in the natural history of CPS (9.7 vs 22.2 years duration epilepsy) than previously reported. The presence of FDG-PET hypometabolism may be associated with a poor response to drug treatment. PET can identify metabolic abnormalities associated with epileptic foci in children and adolescents and is useful in directing surgical intervention for the control of refractory complex partial epilepsy.

Adolescent↗
PubMed1995

Mutation of the p53 gene precedes aneuploid clonal divergence in colorectal carcinoma.

To establish whether p53 mutation precedes or follows clonal divergence in human colorectal carcinomas, 17 tumours were analysed at multiple sites (2-5 each) for single-strand conformation polymorphisms (SSCP) within exons 5-8 of the p53 gene. A previous study had demonstrated subclones of differing DNA ploidy in these tumours, but all showed immunocytochemical evidence for p53 stabilisation, using the monoclonal antibody PAb 1801. Mutations within exons 5-8 of p53 were identified by the presence of an abnormally migrating band in 10 of the 17 carcinomas: five in exon 5, four in exon 7 and one in exon 8. In each of these positive cases, samples from different parts of the carcinoma showed identical gel migration patterns in SSCP analysis. Similarly, the remaining seven tumours were concordant for absence of band shift across all samples of each tumour. Six SSCP-positive cases contained multiple populations differing in DNA ploidy, while four were homogeneously diploid or aneuploid throughout. Very similar proportions were observed in the SSCP-negative cases. In four positive tumours the mutation was confirmed by sequencing or through alteration of nucleotide-specific restriction enzyme cleavage. Identical mutations appeared in every sample from the same tumour. The results provide unequivocal evidence that the same mutant allele of p53 is present throughout each tumour bearing a mutation, regardless of the clonal variation identified by analysis of DNA ploidy. We conclude that in colorectal tumorigenesis mutation of p53 occurs as a single event which precedes and may facilitate the aneuploid clonal divergence of carcinomas.

Alleles↗
PubMed1995

A mutation in the alpha tropomyosin gene TPM3 associated with autosomal dominant nemaline myopathy.

Nemaline myopathies are diseases characterized by the presence in muscle fibres of pathognomonic rod bodies. These are composed largely of alpha-actinin and actin. We have identified a missense mutation in the alpha-tropomyosin gene, TPM3, which segregates completely with the disease in a family whose autosomal dominant nemaline myopathy we had previously localized to chromosome 1p13-q25. The mutation substitutes an arginine residue for a highly conserved methionine in a putative actin-binding site near the N terminus of the alpha-tropomyosin. The mutation may strengthen tropomyosin - actin binding, leading to rod body formation, by adding a further basic residue to the postulated actin-binding motif.

Amino Acid Sequence↗